Racing pioneer, inventor, and world-class horn dog Smokey Yunick (read his autobiography "Best Damn Garage in Town" if you don't believe the horn dog part) proved that every 10-degree reduction in inlet-air temperature has the potential of increasing engine output by 1 percent. While this may not seem like much, let's crunch the numbers and take a second look.

It all starts with realizing that even though the ambient air temperature--the air you breathe in the driver seat--may be a comfortable 80 degrees F, the engine-compartment air temperature beneath an unvented hood is well in excess of 180 degrees F thanks to the heat radiated by the engine, exhaust headers, manifolds, and cooling system. That's a 100-degree difference in the air temperature above and below the skin of the hood.

What if you broke through the hood and took advantage of that cooler outside ambient air temperature? By Smokey's account, you'd reduce inlet-air temperature by 100 degrees and see a 10 percent increase in horsepower. So, in theory if you're making 400 hp breathing underhood air, you'd get 440 with outside air thanks to its greater density. Is it free horsepower? Yes and no. Yes, in that we don't have to lay a finger on the engine to see gains. No in that there is always an aerodynamic penalty (increased drag) any time appendages sprout from the vehicle surface. Regardless, the scoop's aerodynamic drag is less than the power increase, so it's a worthwhile trade-off.

As with everything we do to our cars, there's a form and function balance that must be respected. There are few things tackier than seedy off-kilter hoodscoops and butchered sheetmetal that look like the work of a pre-Sharon Ozzy wielding a rotary axe. In this how-to, we'll explore some tricks to help you cut the hood and mount the scoop so it looks professional.